Bragg-Williams Model of Ordered B2, L12 and L10 Type Binary Intermetallic Compounds Containing Point Defects

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Addis Ababa Universty


Ordered intermetallic compounds draw great interest at the present time because of both possible applications and fundamental scientific importance. The scientific interest is derived from the recognition that many intermetallics exhibit considerable ranges of nonstoichiometry which correspond to the presence of constitutional point defects which are temperature independent. Additional to these constitutional point defects thermally activated point defects can occur. The total defect structure (i.e. the types and the concentrations of the point defects) determines important properties of the intermetallic compounds (e.g. all diffusion dependent properties). Hence, for understanding and control of these properties a detailed knowledge of the defect structure in intermetallic compounds as function of composition and temperature within the homogeneity range of the compounds is a prerequisite. This thesis is aimed at formulating a model which can be used to calculating the ordering energy parameters ΔHAB and ΔHB□, and the concentration of vacancy (z) and the concentration of Antistructure Defect as a function of the composition parameter χ and the temperature T. The ordering energy is related to but different from the formation energy, because the former is the energy change from the disordered alloy AB to the ordered alloy AB, while the latter is the energy change from the pure metals A and B to the ordered AB. Having obtained the model parameters (note that these are H ij and S ij for the fitting of the vacancy concentration and hij and sij for the fitting of the thermodynamic properties, respectively), the temperature dependence of the vacancy concentration can also be determined.



Ordered intermetallic compounds